全文获取类型
收费全文 | 28071篇 |
免费 | 4019篇 |
国内免费 | 2770篇 |
专业分类
电工技术 | 3832篇 |
技术理论 | 3篇 |
综合类 | 3756篇 |
化学工业 | 2812篇 |
金属工艺 | 834篇 |
机械仪表 | 1385篇 |
建筑科学 | 1834篇 |
矿业工程 | 734篇 |
能源动力 | 900篇 |
轻工业 | 749篇 |
水利工程 | 767篇 |
石油天然气 | 847篇 |
武器工业 | 729篇 |
无线电 | 4272篇 |
一般工业技术 | 2973篇 |
冶金工业 | 842篇 |
原子能技术 | 482篇 |
自动化技术 | 7109篇 |
出版年
2024年 | 71篇 |
2023年 | 439篇 |
2022年 | 621篇 |
2021年 | 806篇 |
2020年 | 1015篇 |
2019年 | 1019篇 |
2018年 | 902篇 |
2017年 | 1134篇 |
2016年 | 1191篇 |
2015年 | 1223篇 |
2014年 | 1656篇 |
2013年 | 1961篇 |
2012年 | 1907篇 |
2011年 | 2071篇 |
2010年 | 1599篇 |
2009年 | 1570篇 |
2008年 | 1644篇 |
2007年 | 1823篇 |
2006年 | 1724篇 |
2005年 | 1493篇 |
2004年 | 1272篇 |
2003年 | 1089篇 |
2002年 | 1026篇 |
2001年 | 846篇 |
2000年 | 740篇 |
1999年 | 647篇 |
1998年 | 475篇 |
1997年 | 452篇 |
1996年 | 362篇 |
1995年 | 342篇 |
1994年 | 337篇 |
1993年 | 282篇 |
1992年 | 211篇 |
1991年 | 156篇 |
1990年 | 152篇 |
1989年 | 112篇 |
1988年 | 91篇 |
1987年 | 52篇 |
1986年 | 44篇 |
1985年 | 38篇 |
1984年 | 41篇 |
1983年 | 37篇 |
1982年 | 31篇 |
1981年 | 16篇 |
1980年 | 19篇 |
1979年 | 20篇 |
1978年 | 12篇 |
1977年 | 9篇 |
1960年 | 7篇 |
1959年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
21.
Ziwen Wu Tianping Zhang 《International Journal of Adaptive Control and Signal Processing》2021,35(9):1768-1788
In this article, the issue of adaptive finite-time dynamic surface control (DSC) is discussed for a class of parameterized nonlinear systems with full state constraints. Using the property of logarithmic function, a one-to-one nonlinear mapping is constructed to transform a constrained system into an unconstrained system with the same structure. The nonlinear filter is constructed to replace the first-order linear filter in the traditional DSC, and the demand on the filter time constant is reduced. Based on finite-time stable theory and using modified DSC, the finite-time controller is designed via DSC. Theoretical analysis shows that all the signals in the closed-loop system are semiglobal practical finite-time stable. Furthermore, none of the states are outside the defined open set. In the end, simulation results are presented to demonstrate the effectiveness of the proposed control schemes with both linear filters and nonlinear filters. 相似文献
22.
Monika Bosacka Anna Blonska-Tabero Elzbieta Filipek Jana Luxová Petra Šulcová 《Ceramics International》2021,47(17):24607-24614
A new pyrophosphate(V) of the formula Co5Cr2(P2O7)4 was obtained in the system Co2P2O7–Cr4(P2O7)3 as a result of solid-state reactions taking place between different reactants. The new compound crystallizes in the orthorhombic system and belongs to the family of pyrophosphates of the general formula M52+M23+(P2O7)4 and is probably isostructural with Fe52+Fe23+(P2O7)4. Powder diffraction pattern, infrared spectrum and SEM image of the new compound were presented. As a new potential inorganic pigment, Co5Cr2(P2O7)4 was tested for its thermal stability, particle size distribution and colour properties, which were studied both for powder and after introduction into organic matrix and leadless ceramic glaze. The colour of Co5Cr2(P2O7)4 powder was defined as deep grey with the colour coordinates L*/a*/b* = 60.63/-1.42/-3.41 and according to the hue angle (h° = 247.39°) it belongs to the blue region. Co5Cr2(P2O7)4, with its relatively high thermal stability (t m = 1230 ± 10 °C) and appropriate colour properties, is a good candidate to be used as inorganic pigment for colouring of acrylic paints. In the case of leadless glaze, the obtained compound acts as a dye. 相似文献
23.
As a highly complex and time-varying process, gas-water two-phase flow is commonly encountered in industries. It has a variety of typical flow states and transition flow states. Accurate identification and monitoring of flow states is not only beneficial to further study of two-phase flow but also helpful for stable operation and economic efficiency of process industry. Combining canonical variate analysis (CVA) and Gaussian mixture model (GMM), a strategy called multi-CVA-GMM is proposed for flow state monitoring in gas-water two-phase flow. CVA is used to extract flow state features from the perspective of correlation between historical data and future data, which solves the cross correlation and temporal correlation of multi-sensor measurement data. GMM calculates the possibility that the current flow state belongs to each typical flow pattern and judges the current flow state by probability indicators. It is conducive to follow-up use of Bayesian inference probability and Mahalanobis distance-based (BID) indicator for flow state monitoring, which avoids repeated traversal of multiple CVA-GMM models and improves the efficiency of the monitoring process. The probability indicators can also be used to analyze transition flow states. The method combining the probabilistic idea of GMM with the deterministic idea of multimodal modeling can accurately identify the current flow state and effectively monitor the evolution of flow state. The multi-CVA-GMM method is validated by using the measured data of the horizontal flow loop of gas-water two-phase flow experimental facility, and its effectiveness is proved. 相似文献
24.
以微型土压平衡(Earth Pressure Balance,EPB)盾构机推进液压系统作为研究对象,介绍了推进系统的工作原理,对混入空气后的油液黏度和有效体积弹性模量进行分析,建立了推进系统数学模型,并对混入不同百分比空气的系统进行仿真运算,得到了液压缸位移响应和速度响应随系统含气量变化的关系。研究表明:随着液压系统空气含量的增加,液压缸位移响应发生迟滞,速度响应变慢,液压缸在运动时产生振动。结合各液压元件工作原理,依次对实际盾构机推进系统元件进行排气,最终排除了液压系统中混入的空气,为实现盾构机平稳推进提供了理论依据。 相似文献
25.
Xueli Chen Ke Liu Qianwan Qin Zhenlu Yu Meiqing Li Xingyu Qu Yu Zhou Aichun Dou Mingru Su Yunjian Liu 《Ceramics International》2021,47(11):15400-15407
With excellent specific capacity, superior cycle stability, safety and strong practical, Nb2O5 has been considered as one of the prospective anode materials for lithium-ion batteries (LIBs). However, current study suggests that Nb2O5 electrode materials for LIBs still face the vital issues of low electrical conductivity and poor rate performance. Therefore, carbon-coated TT-Nb2O5 materials are designed and synthesized through solid state method in this work, which present high specific capacity (228 mA h g?1 at 0.2C), satisfactory rate properties (107 mA h g?1 at 20 C). The outstanding electrochemical property can not only give the credit to the pseudocapacitance effect of TT-Nb2O5, but also attribute to introduction of carbon. The homogeneous carbon-coated materials enhance the electrical conductivity, increase the electron transmission speed and alleviate particle crushing. This research not only offers a new method for preparing excellent electrode materials, but also provides a kind of excellent anode material with prospective application for LIBs. 相似文献
26.
27.
Yingcai Bi Menglu Lan Jiaxin Li Shupeng Lai Ben M. Chen 《Asian journal of control》2019,21(4):1732-1744
Micro Aerial Vehicles (MAVs) have great potentials to be applied for indoor search and rescue missions. In this paper, we propose a modular lightweight design of an autonomous MAV with integrated hardware and software. The MAV is equipped with the 2D laser scanner, camera, mission computer and flight controller, running all the computation onboard in real time. The onboard perception system includes a laser‐based SLAM module and a custom‐designed visual detection module. A dual Kalman filter design provides robust state estimation by multiple sensor fusion. Specifically, the fusion module provides robust altitude measurement in the circumstance of surface changing. In addition, indoor‐outdoor transition is explicitly handled by the fusion module. In order to efficiently navigate through obstacles and adapt to multiple tasks, a task tree‐based mission planning method is seamlessly integrated with path planning and control modules. The MAV is capable of searching and rescuing victims from unknown indoor environments effectively. It was validated by our award‐winning performance at the 2017 International Micro Air Vehicle Competition (IMAV 2017), held in Toulouse, France. The performance video is available on https://youtu.be/8H19ppS_VXM . 相似文献
28.
The potential energy profile of the reaction between dimethyl disulfide and OH? radicals is explored by utilizing ab initio and hybrid meta density functional theory methods. Having the energies and structural data of the stationary points, statistical rate theories, such as transition state theory and variable reaction coordinate-transition state theory, are employed to compute the overall rate constants, and discuss the mechanism and product channels. On the basis of the calculations, the overall rate coefficient is predicted to be 2.49?×?10?10?cm3?molecule?1?s?1 at 298?K. It is found that in the most favorable pathway, the reaction proceeds via formation of the relatively unstable intermediate CH3S?(OH)SCH3 decomposing rapidly to yield CH3S?+CH3SOH. 相似文献
29.
Manish Aggarwal 《国际智能系统杂志》2019,34(7):1524-1554
A new family of attitudinal discrete choice models is proposed by considering the attitudinal character and the weight vector, both of which are specific to a decision maker (DM). Given the attribute values of different alternatives, the proposed models give varying choice probabilities, as per the DM's-specific attitudinal character and the weight vector. It is also shown that the conventional discrete choice models are the special cases of the proposed attitudinal models. The proposed choice models are also generalized through an additional parameter to add to their capabilities. An application on real data is included to demonstrate their usefulness in the real world. 相似文献
30.
Yohannes Eneyew Ayalew 《Information & Communications Technology Law》2019,28(2):208-224
Freedom of expression is a foundational stone for democracy and embraces a number of other rights, including – freedom to seek, receive, and impart information using any medium. Around 16 million Ethiopians, comprising 15.4% of the total population, use the Internet. The Ethiopian Internet shutdown saga has been marked by competing narratives. On one hand, the government has been using two governing narratives, i.e. national security narrative and ‘economic growth’ narrative to justify shutdowns of the Internet. But, the individuals’ self-expressions on social media find itself as competing narrative. Since 2016, the Internet has been closed more than six times under the cloak of national security, quelling rising protests, controlling strikes, and exam cheating. As such, freedom of expression of millions has been muzzled. The article argues blanket Internet shutdowns do not meet the caveats of human rights law. 相似文献